In an optical disk apparatus such as a CD-R drive, a LD (laser diode) irradiates a recording power no less than a reproduction power on an optical disk to form pits thereon while a rotational velocity of the optical disk is controlled at a constant linear velocity (CLV), and data is thus recorded. To optimize the recording power, techniques such as OPC (Optimum Power Control) and ROPC (Running Optimum Power Control) are used. In OPC, the recording power is changed in a plurality of steps (15 steps, for example) to perform test writing on a predetermined position (a test area or a power control area) of the optical disk, test writing data is reproduced to select a recording power having the best reproduction quality (β value, for example). The β value is calculated by the formula: β=(a−b)/(a+b) where ‘a’ is a peak value and ‘b’ is a bottom value of a reproduction RF signal envelope, and the β value is regarded to be optimum when it is within a predetermined range (0.04 to 0.05, for example).
On the other hand, even if the recording power is optimized using OPC, there are cases where recording sensitivity scatters along an optical disk plane due to the influence of recording film characteristics on the optical disk plane, warping, or the like. An OPC technique only decides the optimum recording power in the predetermined position of the optical disk, and there is no guarantee that data can be recorded with the same quality at other positions. ROPC deals with such varied characteristics by sampling a reflected light quantity from the optical disk in forming pits with the recording power and performs feedback control to the recording power to bring the reflected light quantity to a constant value.
Although OPC and ROPC enable control of the recording power to record data in the case of CLV control, even if such control is directly executed high quality recording is not possible with constant angular velocity (CAV) control because the linear velocity changes in accordance with a radius position of the optical disk.
Japanese Patent Laid-Open Publication No. Hei 11-296858 describes an attempted solution wherein the recording power is changed in accordance with the linear velocity in CAV control. Specifically, the recording power is increased approximately proportional to clock frequency for recording, which corresponds to the linear velocity.
Further, Japanese Patent Laid-Open Publication No. Hei 10-106009 describes correction of optimum recording power value determined through OPC in accordance with the linear velocity. Specifically, a correction coefficient is found for every wobble signal frequency proportional to the linear velocity, and the optimum recording power decided by the OPC is multiplied by the correction coefficient that corresponds to the wobble signal frequency during recording to correct the recording power.
The foregoing gazette also describes that the recording power is controlled using CAV control to bring the reflected light quantity of the recording power to a constant value always.
However, even if the recording power is adjusted in consideration of the linear velocity, optimum recording is not necessarily performed due to the variation of characteristics along the optical disk plane, and thus control similar to ROPC is also required with CAV.
On the other hand, by controlling the recording power to maintain a constant power of reflected light, a sequential feedback control such as ROPC is made possible. However, in the Japanese Patent Laid-Open Publication No. Hei 10-106009, the recording power is only controlled such that a reflected light quantity level is brought to a predetermined constant value, which is not sufficient. In other words, because the linear velocity increases at an outer circumferential area, recording sensitivity is reduced, a greater recording power is required and the quantity of reflected light generally increases accordingly. Therefore, in forming pits similar to those in an inner circumference in the outer circumference having the greater linear velocity, the intensity of reflected light after the pits have been formed should increase with the increase of recording power in the outer circumference having the greater linear velocity. Then, if the reflected light intensity is controlled to maintain to the same level as that of the inner circumference, excessive laser power, also referred to as ‘over baking’ is caused.
FIG. 9 shows level changes of the intensity of the light reflected at the inner circumferential area and the outer circumferential area when forming pits using a laser of recording power. In the drawing, level B shows the intensity of recording power light reflected after formation of pits. In the technique described in the Japanese Patent Laid-Open Publication No. Hei 10-106009, because the recording power is controlled to bring level B to the constant level in the inner circumference and the outer circumference, under normal circumstances the laser power becomes excessive and forms excessive pits and the value of level B becomes smaller as shown by the chain line than a primary value shown by the solid line, where the value of level B in the outer circumferential area is supposed to be greater than that of the inner circumferential area as shown by the solid line (when the same pits are formed in the inner circumference and the outer circumference, the outer circumferential area has greater reflected light quantity for the recording power is greater). As a result, optimum waveform for data reproduction cannot be obtained.